Moonflower Vines & Hornworms

Moonflower vines make fragrant evening displays.

Massive, funnel-shaped white blooms that perfume the evening air are moonflower (Ipomoea alba) vine's contributions to the summer and fall garden. The 6-inch, white flowers brighten the twilight as they unfurl against the vine's deep green, round to oval leaves. They remain open through the night before closing by noon of the following day. Like many nightshade family plants, this quickly growing tropical vine is a food source for hungry tobacco hornworm caterpillars.

Carolina Sphinx Moth

Adult Carolina sphinx moths (Manduca sexta) feed on nectar and lay their eggs on the vine's foliage. They deposit the white to pale green eggs on the upper surfaces of the vine's lower leaves. These moths are up to 4 inches across, with yellow or orange spots on gray to brown bodies. Their range covers much of the eastern United States, but they are most common along the Gulf Coast.

Sphinx Moth Hornworms

The Carolina sphinx moth, or tobacco, hornworm hatches in two and eight days. The red, pointed appendage on its tail accounts for the worm's name. The eight-legged caterpillar's green, cylindrical body has distinctive, diagonal black and white stripes. The worm feeds on moonflower foliage for about three weeks before dropping to the ground, tunneling into the soil and spinning its cocoon. The cocoons normally measure close to 2 inches long.

Life Cycle

Carolina sphinx moths and their larvae breed and feed on moonflower vines during the midsummer and fall blooming season. The time it takes between when the larvae hatch and adult moths emerge from cocoons depends on temperature. The entire cycle takes between four and six weeks in most environments. The moths produce three or four generations each year in Florida and other Gulf Coast states. Cooler summer climates limit their reproduction to one or two generations, report Clemson University Extension's Aaron Eichman and his colleagues.

Natural Hornworm Control

Roto-tilling the soil to a depth of 4 inches around your moonflower vine destroys the buried cocoons. Hand removal of light hornworm infestations is sufficient. Drown the worms in water or dissect them with garden shears. Hornworms also are vulnerable to parasitic wasp infestation. The wasps' larvae cover the worms with white cocoons and emerge as adults to feed on them. Let infested worms remain on the vine so the newly hatched wasps will attack healthy ones.

Hornworm Pesticides

Bacillus thuringiensis-based pesticides contain bacteria that paralyze the worms' digestive systems shortly after they feed on moonflower foliage. The affected worms eventually starve to death. Spinosad-, carbaryl- and permethrin-based chemical insecticides are somewhat effective in controlling hornworms. These treatments work best on the young larvae. Older caterpillars have increased pesticide resistance.

References

• Missouri Botanical Garden Kemper Center for Home Gardening: Ipomoea Alba
• Colorado State University Extension: Hornworms and "Hummingbird Moths"; W.S. Cranshaw; Feb. 2007
• Colorado State University Extension: The Tomato Hornworms; Judy Sedbrook
• Clemson University Department of Entomology: Manduca Sexta "Tobacco Hornworm/Carolina Sphinx Moth"; Aaron Eichman et al.; Fall 2000
• Utah State University Extension: Tomato and Tobacco Hornworms; Jay B. Karren; November 1999

Resources

• Cornell University: Moonflower